‘KinnowLS’ is a mandarin selection developed at Riverside, Calif. and derived from an irradiated bud of the diploid mandarin cultivar ‘Kinnow’ (unpatented), a mid-to-late season maturing variety. ‘Kinnow’ is a hybrid of two Citrus cultivars, ‘King’ (unpatented, Citrus reticulata ‘Blanco’) and ‘Willowleaf’ (unpatented, Citrus reticulata ‘Blanco’), which was first developed by H. B. Frost in Riverside, Calif. After evaluation, the ‘Kinnow’ was released as a new variety for commercial cultivation in 1935.
Irradiation of budwood from registered ‘Kinnow’ trees in Exeter, Calif., was accomplished in June of 1997 in Riverside, Calif. Specifically, irradiation of 150 buds of ‘Kinnow’ mandarin was accomplished using 40 Gray units of gamma irradiation from a Cobalt-60 irradiation source. Buds from this irradiation were propagated onto Carrizo rootstocks in a greenhouse in Exeter, Calif. where they were grown to field-plantable-sized trees. Out of these irradiations, a total of 73 trees were obtained. This low yield of trees is typical because the radiation kills many of the buds. These trees were then planted in May 1998 in Exeter, Calif. Fruit production and evaluation began in 2001. One selection from this irradiated population (propagated on Carrizo rootstock) distinguished itself from the others in having tree growth typical of ‘Kinnow’ mandarin, very low seed counts in comparison to the original ‘Kinnow’ cultivar, and excellent fruit quality and normal fruit production characteristic of the ‘Kinnow’ parent. After two seasons of fruiting, this selection was given the name ‘Kinnow IR5’ and selected for further trials. In January 2003, buds of this selection were taken and propagated onto Carrizo and C35 citrange rootstock for field trials. In June of 2004, 72 trees, produced in Exeter, Calif., were planted at six sites (twelve trees at each site): Arvin, Irvine, Lindcove, Thermal, Riverside, and Woodlake, Calif. All trials were propagated equally on Carrizo and C35 citrange rootstocks. All trials were in mixed-plantings with other cultivars, including seedy cultivars with high pollen viability. Fruit production of these propagated trees commenced in 2006 (a few trees at each site) and 2007 (all trees at all sites). In October 2008, budwood from the selected tree was sent to Exeter, Calif. for evaluation of disease status and, as needed, elimination of viruses and other pathogens. Six trees were then established as disease-free ‘mother’ trees in a greenhouse in Exeter, Calif. The properties of ‘KinnowLS’ were found to be true to type and transmissible by asexual reproduction in comparing these plantings with the original ‘KinnowLS’ selection.